1. Field of the Invention
The present invention relates to a premises gateway device, more particularly, to a premises gateway device that realizes connection between a home network and the Internet which is a public network.
2. Description of the Related Art
In recent years, along with improvement in an Internet access technology, home networks have evolved markedly. Access to web sites at a personal computer (PC) and transfer of mails are previously the main usages of the home network. The features of a network at home have diversified. Using the network, for example, an inexpensive telephony service based on the Voice-over-IP (VoIP) technology is received, a bidirectional data communication service is received over the Internet through a television broadcast, or a home appliance such as an air conditioner or a refrigerator or lightings including fluorescent lamps are controlled outdoors over the Internet. The role of a premises gateway device to be used to connect the pieces of equipment onto the Internet has become pivotal.
The premises gateway device interconnects such pieces of equipment as a PC, a telephone, a home appliance, and lightings which constitute the foregoing home network, and transmits or receives data to or from an Internet service provider (ISP) via an optical network unit (ONU) that is subscriber-side equipment, an optical line terminator (OLT) that is station-side equipment, and a carrier network which constitute a passive optical network (PON) system. The ISP connects the premises gateway device onto the Internet or a public switched telephone network (PSTN) via a VoIP gateway according to the type of data. For connection between each household and the ISP, the PPP-over-Ethernet (PPPoE) that is a protocol providing a pseudo point-to-point network has often been employed. In recent years, the IPsec that is a protocol providing a standard feature for the IP Version 6 (IPv6) has been used to form an IPsec tunnel between the premises gateway device and the ISP so that each of the pieces of equipment at home and the ISP can safely transfer data to or from each other. The premises gateway device encapsulates and encrypts data sent from premises network equipment and transfers the data to the ISP, or decrypts and decapsulates data sent from the ISP and transfers the data to the home network equipment. Data encrypting/decrypting processing has to be performed on all data items to be treated, and a processing time largely depends on a data rate. What is referred to as the data rate refers to an amount of data per a unit time.
The throughput of the premises gateway device is proportional to the operating frequency of a processor as long as the same type of processor is taken into account. Therefore, in the premises gateway device, the processor operates at a frequency at which the throughput permitting data to be treated at the highest data rate that should be guaranteed under the specifications for the premises gateway device can be realized. With the advent of the PON system, the baud rate on an access network linking each household and a carrier station exceeds 1 gigabits/sec and is getting higher. Accordingly, the throughput requested for the premises gateway device is getting higher day by day. The premises gateway device realized a telephoning function and a function of controlling a home appliance outdoors. For example, for the telephoning function, the power supply of the premises gateway device cannot be turned off in order to treat an incoming call that occurs at an unknown time instant. For controlling a home appliance outdoors, the power supply of the premises gateway device cannot be turned off in order to receive control data at a time at which a user is not at home. The premises gateway device has to operate all the time. The power consumption required for the premises gateway device to stand by poses a non-negligible problem.
As a technique for reducing the power consumption required for the premises gateway device to stand by, there is a technique disclosed in, for example, JP-A-2002-319956. According to the technique, the gateway device is separated into a system 1 having the minimum necessary features for connection onto the Internet, and a system 2 having the features needed to run applications. The power supplies of the systems 1 and 2 are turned on or off in order to realize reduction in power consumption in a standby state.
In contrast, as a technique for dynamically varying the operating frequency of a processor, there is a technique disclosed in, for example, JP-A-2004-280216. According to the technique, a clock frequency optimal for running of an application program is varied depending on a load imposed on the processor during the previous run, and the clock frequency is thus finely controlled.